It has become common practice in recent years for cosmetic formulations such as skin creams to contain liposomes. Liposomes are small sacs formed from certain surface active molecules, most commonly phospholipids, which in aqueous media arrange themselves into a bi-layered membrane defining a microscopic closed vesicle. Liposomes are commonly employed in moisturising creams because they enhance the delivery of water to the skin.
It is also known to deliver therapeutic agents to the skin in microcapsules, in particular by encapsulating the therapeutic agent in liposomes. For example, EP-A-0224837 (Rohm Pharma GmbH) discloses compositions for treating skin disorders in which the active ingredient is encapsulated in liposomes comprising lecithin and cholesterol. WO85/03640 (The Liposome Company, Inc.) discloses pharmaceutical formulations which may be topically applied and in which . liposomes are held in a gel matrix to provide improved retention and sustained release of entrapped bioactive agents at the site of application.
It is also known to use liposomes to target therapeutic agents to target sites within the body. In general, a molecule which binds specifically at the target site is attached to the liposome to target the therapeutic agent to the appropriate site. For example, EP-A-036277 (Regents of the University of California) discloses a method for attaching to liposomes proteins, such as antibodies or antibody fragments, which bind specifically to a target site. In particular, the reference is concerned with targeting cytotoxic drugs to tumours in the body.
WO87/07150 (The John Hopkins University) discloses pharmaceutical compositions which comprise nanoparticles, of which liposomes are one example, which are targeted by means of surface site-directing molecules capable of binding cell receptors and which are, themselves, therapeutic or pharmacologic agents. Although the reference makes passing reference to topical application, it is primarily concerned with treating, or performing diagnosis on, diseased inner organs or tissues.
Similarly, W088/00824 contemplates targeting liposomes containing therapeutic agents to mucosal surfaces by means of positively charged groups at the surface of the liposomes.
The benefits which may be obtained by directing particles including cosmetically-effective benefit agents to target: sites on the skin and/or the hair do not appear to have been appreciated to date.